The present invention relates to systems for transporting high solids materials such as concrete and sludge. In particular, the present invention relates to a material pump system in which a positive displacement pump, with a pivoting transfer tube valve which connects pump cylinders to the pump outlet, conveys material through a pipeline with a valve located downstream of the pump, and in which the pumping rate and accumulated volume of material pumped are automatically determined.
Positive displacement pumps are frequently used for conveying concrete, sludge and other materials through pipelines in municipal, industrial and construction applications. Positive displacement pumps offer a number of significant advantages over screw or belt conveyors in the pumping of materials. For example, positive displacement pumps are capable of pumping thick, heavy materials which may not be practical for belt or screw conveyors. Pump and pipeline systems also take up less space than screw or belt conveyors and, with the use of simple elbow pipes, are capable of transporting material around corners. Additionally, positive displacement pumps offer a reduction in noise over mechanical conveyors as well as greater cleanliness and reduced spillage.
Various state and federal regulations covering the processing and disposal of sludge require that the processor accurately measure and record the amount of material handled. Similarly, in concrete pumping applications, it is becoming increasingly necessary to accurately measure the quantity of concrete pumped. The pumping of concrete causes considerable wear on the components of the concrete pump and pipeline. Accurate measurement of the quantities of concrete pumped allows the proper maintenance and replacement of components to be scheduled prior to a component failure during use. This prevents unnecessary and costly losses of time due to system failures as well as the inefficient waste of concrete which may become unusable as a result of the delays associated with the failure of a pump or pipeline component.
Positive displacement material pumps such as those described in Oakley et al., U.S. Pat. No. 5,106,272, entitled "SLUDGE FLOW MEASURING SYSTEM", can accurately measure the volume of material transported. Oakley et al. discloses a system for transporting high solids sludge which includes a positive displacement pump for pumping sludge through a pipeline. The volume of sludge transported is accurately measured by determining the fill percentage of the pumping cylinder during each pumping cycle. The fill percentage is determined by using any of a number of sensed parameters including material flow signals, measured time intervals, hydraulic fluid pressure, and hydraulic fluid flow rate during each pumping cycle.
One embodiment of the system and pump disclosed in Oakley et al. includes a valve, commonly referred to as a poppet valve, between the pumping cylinder and the outlet which opens and connects the pumping cylinder to the outlet only when the pressure within the pumping cylinder essentially equals the pressure at the outlet. The timing of the opening of the outlet poppet valve during the outlet stroke provides a means for determining the fill percentage or the total volume delivered during each pumping stroke.
Oakley et al. also discloses another embodiment of the system in which the pump includes an outlet valve, commonly referred to as a pivoting transfer tube valve, which connects the outlet to the pumping cylinder during the entire pumping stroke. In this embodiment, both the hydraulic pressure driving the piston and the outlet pressure are sensed during the pumping stroke. Determining either the time or the piston position in the pumping stroke when the hydraulic pressure equals the outlet pressure can be used to derive a fill percentage or volume delivered during each pumping stroke.
When pumping concrete or other material with large particles, material pumps frequently employ pivoting transfer tube valves, like those disclosed in Oakley et al., to control the intake and outlet of material to and from the pump cylinders. Pivoting transfer tubes switch hydraulically to connect the pump cylinders to either a material intake or a material outlet of the pump. In a two-cylinder material pump, the transfer tube switches hydraulically to serve both pumping cylinders. The transfer tube is mounted in an open-topped housing or hopper which accepts the material to be pumped. The transfer tube pivots to connect the pumping cylinder to the pump outlet and pipeline, while allowing the cylinder which is intaking material to pump material from the hopper into the cylinder.
Pivoting transfer tubes have several advantages over other valve types. First, as the transfer tube switches, large particles which could interfere with the pump performance are moved or sheared. Second, the transfer tube's large diameter allows it to accept larger particles than other types of valves. Finally, transfer tubes have automatic adjustment capability and low maintenance requirements as well as a wear-life unaffected by pumping pressures.
In a typical application, a concrete pump with a pivoting transfer tube valve may be used to pump concrete for construction of a high-rise building. In such applications, the pump is frequently connected to a long pipeline which carries the concrete to its destination. After completion of a pumping stroke in one cylinder, as the transfer tube switches to connect another cylinder to the pump outlet, the material in the pipeline exerts extreme pressure back towards the hopper. In addition to working against the concrete pump's purpose of pumping concrete through the pipeline, this can create an extremely dangerous condition as the concrete is forced back through the pipeline toward the pump.